1. Field of the Invention
The present invention relates to a two-evaporator refrigeration system employing novel, highly efficient working fluid mixtures, designed to cool two separate compartments at different temperatures in the same device (e.g., as in a refrigerator/freezer unit). The novel working fluid mixtures of the present invention are specifically designed for a two-evaporator refrigeration system.
2. Prior Art
It is well known in the art that mixtures of fluids can be more efficient in a refrigeration cycle than a single refrigerant employed alone.
A dual evaporator system employing a binary refrigerant is disclosed by Wilson et al (U.S. Pat. No. 4,416,119) for use in a refrigerator/freezer. The circuit employs alternating evaporators and heat exchangers, thus requiring exactly two heat exchangers. Other elements, e.g., a separator and a rectifier, are further required in the system disclosed by Wilson et al. Also disclosed is a mixture of R22 (monochlorodifluoromethane) and R114 (1,2-dichloro-1,1,2,2-tetrafluoroethane) as the refrigerant, but a non-azeotropic mixture of R12 (dichlorodifluoromethane) and R11 (trichloromonofluoromethane) is particularly preferred.
One condition under which a working fluid mixture can be more efficient than any of the single components thereof is identified by Vobach (U.S. Pat. Nos. 4,707,996 and 4,674,297), wherein a mixture of a low-boiling refrigerant, such as R22 or R32 (difluoromethane), and a high-boiling solvent, such as 1,1,1-trichloroethane, exhibits a negative deviation from Raoult's Law.
Another condition where a mixture of refrigerants can be more efficient is disclosed by Rojey (U.S. Pat. Nos. 4,350,020 and 4,344,292), wherein a difference of greater than or equal to 20.degree. C. in the critical temperature exists between the two components of the mixture. The preferred mixture in this case was R22 and R114.